Process for the separate recovery of potassium chloride and sodium chloride from a solid mixture thereof

ABSTRACT

In the process of separating sylvinite into its components potassium chloride from sodium chloride by froth flotation, in which potassium chloride is recovered in the tops and sodium chloride is left in the bottoms, the potassium chloride yield is increased, and its contamination with sodium chloride diminished, by the pressure of a sodium chloride crystal habit modifier in the flotation system. The modifier can be added to the flotation, or to the sylvinite, or even to carnallite before its decomposition into magnesium chloride and sylvinite.

United States Patent 11 1 Becker et al.

1 PROCESS FOR THE SEPARATE RECOVERY OF POTASSIUM CHLORIDE AND SODIUM CHLORIDE FROM A SOLID MIXTURE THEREOF [75] Inventors: Alan M. Becker; Joseph A. Epstein; Michael S. Lupin; Shaul Zolotov, all

of Beer-Sheba, Israel [73] Assignee: Dead Sea Works Ltd., Beer-Sheba,

Israel [22] Filed: July 11, 1973 [21] App]. No.: 378,309

[30] Foreign Application Priority Data July 28, 1972 Israel 40016 [52] US. Cl. 209/166 [51] Int. Cl 803d 1/02 [58] Field of Search 209/166, 167

[56] References Cited UNITED STATES PATENTS 2,177,985 10/1939 Narris 2091166 [4 1 June 24, 1975 2,288,497 6/1942 Tartaron 209/166 X 2,364,520 12/1944 Cole 209/166 2,365,805 12/1944 Cole 209/166 2,468,755 5/1949 N0err..,..... 209/166 X 2,696,912 12/1954 Atwood 209/166 2,702,121 2/1955 Colin 209/166 2,937,751 5/1960 Schoeld 209/166 3,009,575 11/1961 Kean 209/166 Primary ExaminerR0bert Halper Attorney, Agent, or Firm-Lester Horwitz [57] ABSTRACT 4 Claims, No Drawings 1 PROCESS FOR THE SEPARATE RECOVERY OF POTASSIUM CHLORIDE AND SODIUM CHLORIDE FROM A SOLID MIXTURE THEREOF This invention relates to the separate recovery of potassium chloride and sodium chloride from a solid mixture thereof.

Mixtures of potassium and sodium chlorides are of common occurrence and are an important source of potassium chloride. The proportions of the two salts in these mixtures are not defined and vary within wide limits, but in spite of this fact the mixtures are commonly referred to as sylvinite as if they were a defined mineral, and they will thus be called herein. Sylvinite may be of various origin: for example it may be mined, or it may be the solid residue which remains when carnallite is decomposed with water and the magnesium chloride has thereby been dissolved. The more valuable component of the sylvinite is the potassium chloride. It is, therefore, customary to separate it from the sodium chloride. This is conventionally done by froth flotation in which the potassium chloride forms the froth or tops, and the sodium chloride the bottoms or tailings. The flotation is carried out with the aid of conventional flotation chemicals. As practiced at present it does not achieve a complete separation of the two salts: a minor proportion of potassium chloride is lost in the bottoms, and an even greater proportion of sodium chloride remains admixed to the potassium chloride in the tops. Since for most uses of potassium chloride the contamination with sodium chloride is undesirable, the tops are subjected to a refining treatment with water which dissolves preferentially the sodium chloride but also removes some potassium chloride. Thus, potassium chloride losses occur not only in the bottoms but from the tops as well.

This invention has the object to improve the separation of potassium chloride and sodium chloride from sylvinite by froth flotation with a view to increasing the yield of potassium chloride.

It has been found, in accordance with this invention, that the potassium chloride contents of the tops are increased, and the potassium chloride contents in the bottoms are decreased, if the sylvinite slurry subjected to froth flotation contains a sodium chloride crystal habit modifier.

The term sodium chloride crystals habit modifier" (herein crystal modifier" for short) is conventional and has a well-defined meaning. It designates a group of substances which, though mostly not interrelated chemically, have this in common that they influence the properties of solid sodium chloride. One of the uses to which they are conventionally put is the prevention of caking of sodium chloride, and this is accompanied, at least in some cases, by a change of the shape of the crystals. The following are substances which, for the purposes of this invention. are to be regarded as crystal modifiers:

Sodium ferrocynaide, potassium ferrocyanide, sodium ferricyanide, potassium ferricyanide, manganese chloride, citric acid, sodium citrate, nitrilotriacetamide hydrochloride, nitrilo-triacetamide hydrosulfate, 3,5-dioxo-l-piperazine acetamide, nitrilodiacetamide monoacetic acid, nitrilo-diacetamide monoacetonitrile, monosodium glutamate, methyl cellulose, gum arabic.

The required proportion of crystal modifier in the flotation slurry is very small, of the order of l to 500 ppm (parts per million). The optimal concentration will be determined for particular working conditions, the parameters to be considered being, for example, the kind of crystal modifier used, the proportion of sodium chloride in the sylvinite to be processed, the concentration of solids in the flotation slurry, the nature of the flotation chemicals used.

It has been found, moreover, that especially good results can in some cases be achieved by the combination of several crystal modifiers. Thus, a combination of sodium ferrocyanide and nitrilo-triacetamide hydrochloride produces a particularly great increase of the potassium chloride yield in the tops even if both modifiers are used in very small quantities.

For refining the enriched tops produced by the flotation process in accordance with this invention, much less water is required than hitherto, owing to the lower sodium chloride contents of the tops, and the potassium chloride loss due to the refining operation is accordingly smaller. However, the tops produced in accordance with the invention are so much enriched in potassium chloride that for some uses of the potassium chloride the diminished sodium chloride content is no longer harmful and the refining operation can be omitted altogether.

Except for the addition of the crystal modifiers the flotation is carried out in a conventional manner, for example, as follows:

Sylvinite containing 55 percent by weight of KCl and 45 percent of NaCl, calculated on a dry basis, is fed to a mixing tank at a rate of 58 tons per hour, concurrently with 300 m lhour of a brine containing (in g./liter): KCl-93; NaCl-l24; MgCl -l38; CaCl,-8.4. To the same tank the following flotation reagents are added:

Noramac (trade name for an aliphatic amine acetate)-l00 g. per ton of sylvinite;

Pine oil 80 g. per ton of sylvinite.

The slurry, containing 13 percent by weight of solids, is fed at a rate of 340 m lhour to Denver-type flotation cells from which there are separated:

Tops: 66 mlhour, containing 47 percent of solids Bottoms: 274 m /hour, containing 3.9 percent of solids.

In a conventional flotation operation, i.e. in the absence of crystal modifiers, the tops contain about 70 percent of KC] and 30 percent of NaCl (calculated dry), and the bottoms 8 to 1 1 percent of KCl and 89 to 92 percent of NaCl.

The tops are passed through a series of drum filters and washing tanks (operated in countercurrent) whereby the KC] content is raised to 96 percent.

By one embodiment of the invention the crystal modifier is added to the sylvinite at a suitable stage before the flotation. If the sylvinite is produced by the aqueous decomposition of carnallite, the crystal modifier may be admixed at any stage of this decomposition operation. The crystal modifier will then be found in the solid sylvinite residue.

By another embodiment of the invention the crystal modifier is added at the flotation stage. Preferably it is admixed to the slurry which contains sylvinite in solution and is saturated with respect to both potassium chloride and sodium chloride, whereafter the slurry should be agitated for a period of time from 5 to 60 Crystal Modifier Added Bottoms amount ppm NaCl KC] dry) nitrilo-triacetamide hydrosulfate 50 94.7 5.3 potassium ferricyanide 25 94.4 5.6 sodium ferrocyanide 5 95.] 4.9 3,5 dioxo-I-piperazine acetamide I 96.3 3.7 nitrilo-diacetamide monoacetic acid I00 95.7 4.3 nitrilo diacetamide monoacetonitrile I00 95.] 4.9

In the tops, a considerable increase of the KC] content is achieved by the crystal modifiers. In the following list the enrichment in KC] is indicated in per cent (dry) of the total solids of the tops. Thus, ifin a conventional flotation the KC] content of the tops has been 70 percent, an increase of 3.4 percent means that the KC] content is raised to 73.4 percent, with a concomitant depression of the NaCl content, which means that less washing is required:

enrichment Additive Amount of KC] added ppm in tops, of

total tops manganese chloride ]0 3.4 50 3.0 I50 3.1 400 4.8 sodium citrate I00 6.] 200 7.3 monosodium glutamate O 9.] I00 9.8 methylcellulose 4.7 S0 5.] citric acid 2.] 50 6.7 gum arabic 50 5.2 sodium ferrocyanide 5 5.] I0 56 25 6.5 [50 Ill] 250 10.2 potassium ferrocyanide 2O 5.] potassium ferricyanide l0 5.3 25 8.4 nitrilo-triacetamide hydrochloride 10 10.6 25 9.2 50 l [.8 100 12.7 150 12.4 200 I5] nitrilo-triacetamide hydrosulfate 50 I0. I 100 l2.9 3,5 dioxo-l-piperazine acetamide 100 4.5 nitrilo-diacetamide monoacetic acid 100 5.0 nitrilo-diacetamide monoacetonitrile l 00 l .0

The figures of the above list indicate enrichment of the tops in KC], but not necessarily an absolute increase of the potassium yield. However, even the absolute KC] yield is increased by the addition of crystal modifiers in accordance with the invention, as is shown by the following table:

Additive Amount added Increase in yield ppm of KC] A ll citric acid 25 L0 sodium ferrocyanide 5 1.4 potassium ferrocyanide 20 L5 potassium ferricyanide 25 L9 nitrilo-triacetamide hydrochloride 200 ].0 mtrilo'triacetamide hydrosulfate 50 I .0 mtrilo-triacetamide hydrosulfate l 00 l .4

3,5 dioxo-l-piperazine acetamide 5.7 nitrilo-diacetamide monoacetic acid 100 L0 nitrilo-diacetamide monoacetonitrile l 00 8.2

By a further feature of the invention it is found that the crystal modifiers may have a synergistic effect. For example, the combination of sodium ferrocyanide (l) with nitrilo-triacetamide hydrochloride (II) achieves a higher enrichment of the tops in KC] with a lesser aggregate quantity of the crystal modifiers than can be obtained with each of them singly (as indicated in the Table above). Thus combinations of (I) and (II) gave the following results:

Amount of (l) Amount of (II) KC] enrichment in pp ppm p y We claim:

1. A method for the separate recovery of potassium chloride and sodium chloride from a solid mixture thereof, comprising preparing an aqueous slurry of said solid mixture embodying at least one sodium chloride crystal habit modifier, selected from the group consisting of sodium ferrocyanide, potassium ferrocyanide, sodium ferricyanide, potassium ferricyanide, manganese chloride, citric acid, sodium citrate, nitrilotriacetamide hydrochloride, nitrilo-triacetamide hydrosulfate, 3,5-dioxo-l-piperazine acetamide, nitrilodiacetamide monoacetic acid, nitrilo-diacetamide monoacetonitrile, monosodium glutamate, methyl cellulose, gum arabic agitating said slurry and allowing said modifier to act on the sodium chloride for at least five minutes, adding flotation reagents to the slurry, inducing a froth flotation separation to occur, and recovering a potassium enriched fraction from the top and a sodium chloride enriched fraction from the bottom.

2. The method of claim 1 wherein a synergistic combination of two sodium chloride crystal habit modifiers is used.

3. The method of claim 2 wherein a combination of sodium ferrocyanide and nitrilo-triacetamide is used.

4. A method according to claim 1 wherein said mixture is sylvinite produced by the decomposition of carnallite, and said modifier is added during said decomposition. 

1. A METHOD FOR THE SEPARATE FOR THE SEPARATE RECOVERY OF POTASSIUM AND SODIUM CHLORIDE FROM A SOLID MIXTURE THEREOF, COMPRISING PREPARING AN AQUEOUS SLURRY OF SAID SOLID MIXTURE EMBODYING AT LEAST ONE SODIUM CHLORIDE CRYSTAL HABIT MODIFIER, SELECTED FROM THE GROUP CONSISTING OF SODIUM FERROCYANIDE, POTASSIUM FERROCYANIDE, SODIUM FERRICYANIDE POTASSIUM FERRICYANIDE, MANGANESE CHLORIDE, CRITRIC ACID, SODIUM CITRATE, NITRILOTRIACETAMIDE HYDROCHLORIDE, NITRILO-TRIACETAMIDE HYDROSULFATE, 3,5-DIOXO-1-PIPERAZING ACETAMIDE, NITRILO-DIACETAMIDE MONOACETIC ACID, NITRILO-DIACETAMIDE MONOACETONITRILE, MONOSODIUM GLUTAMATE, METHYL CELLULOSE, GUM ARABIC AGITATING SAID SLURRY AND ALLOWING SAID MODIFIER TO ACT ON THE SODIUM CHLORIDE FOR AT LEAST FIVE MINUTES, ADDING FLUTATION REAGENTS TO THE SLURRY, INDUCING A FORTH FLOTATION SEPARATION TO OCCUR, AND RECOVERING A POTASSIUM ENRICHED FRACTION FROM TOP AND A SODIUM CHLORIDE ENRICHED FRACTION FROM THE BOTTOM.
 2. The method of claim 1 wherein a synergistic combination of two sodium chloride crystal habit modifiers is used.
 3. The method of claim 2 wherein a combination of sodium ferrocyanide and nitrilo-triacetamide is used.
 4. A method according to claim 1 wherein said mixture is sylvinite produced by the decomposition of carnallite, and said modifier is added during said decomposition. 